1. Technical Field Relating to the Invention
The present invention relates to a complex digital signal compression device, a method, and a computer-readable storage medium, a complex digital signal expansion device, a method, and a computer-readable storage medium, and a communication device.
For example, the present invention can be applied to a cloud wireless access network where a base station configuration is divided into a Remote Radio Head (RRH) accommodating a user equipment (UE) and a Base Band Unit (BBU).
2. Background of Related Art
In the cloud wireless access network, connection is made via the link of a general-purpose interface such as a CPRI (Common Public Radio Interface) between a first communication device, which the above-mentioned RRH corresponds to, and a second communication device, which the BBU corresponds to. In the CPRI, between the first communication device and the second communication device, a complex digital signal (a complex baseband signal) is exchanged, which is an upstream signal or a downstream signal. In the CPRI, it is not specified that a compressed complex digital signal is exchanged, but it has been proposed that one transmits a compressed complex digital signal to a CPRI link and the other expands the compressed signal to restore an original complex digital signal.
Conventionally, when a complex digital signal is compressed, compression has been performed individually on the real number component and the imaginary number component of the complex digital signal. In a technology described in Non-Patent Document 1 (Karl F. Nieman and Brian L. Evans, “Time-Domain Compression of Complex-Baseband LTE Signals for Cloud Radio Access Networks”, 2013 Proc. IEEE Global Conference on Signal and Information Processing, December, 2013), the numbers of bits of a real number component and an imaginary number component after analog/digital conversion are respectively compressed to one-third, i.e. from 15 bits to 5 bits, by using re-quantization with a noise-shape filter and rate conversion. Moreover, in a technology described in Non-Patent Document 2(Akira Agata, Shinobu Nanba, “A Study on the Baseband Signal Compression Scheme for Base Stations in Cellular Networks”, 2013 The Institute of Electronics, Information and Communication Engineers, General Conference, B-8-9, March, 2013), the numbers of bits of a real number component and an imaginary number component after analog/digital conversion are respectively compressed to one-half by using means, which reduces the number of bits from 16 bits to 14 bits, and Free Lossless Audio Codec, which is an audio compression technology.